Various industrial operations such as coating applications are effected in a chamber filled with inert gas which, quite frequently, is held at sub-atmospheric pressure. Such controlled atmosphere operations include chemical and vapor deposition processes, election beam welding and the like. Another process requiring a chamber is the coating of parts, e.g., turbine blades, by means of plasma spraying in low pressure inert atmosphere as described, for example, in U.S. Pat. No. 3,839,618.
Practical utilization of such a work chamber requires some efficiency in the loading and unloading of workpieces into and out of the chamber. Simply opening up the chamber to change workpieces may be acceptable in the laboratory but is slow in commercial operations because of the time needed for repumping and, in some cases, degassing to eliminate contaminants.
Use of a vacuum interlock is common, involving a smaller auxiliary chamber attached to the main work chamber with an inner door therebetween. The auxiliary chamber is opened with another door to the atmosphere, a workpiece is placed inside, the auxiliary chamber is closed and pumped down, the inner door is opened and the workpiece moved into the work chamber. The process is reversed for removal and then the cycle is repeated for additional workpieces. Since only one workpiece can be handled at a time, such vacuum interlocks are still quite slow to use. An additional problem is the extra time that may be required for the workpiece to cool after being heated during an operation such as plasma spray coating. Cooling may be necessary before opening to the atmosphere to avoid high temperature oxidation and to allow handling.
Other resolutions to the loading problem include the loading of a number of workpieces on a magazine in the work chamber. This approach has been suitable for certain types of operations such as vapor deposition where a large number of workpieces may be coated simultaneously, or where parts are small and/or easily handled. However, magazines loaded with a large number of parts are not very practical for complex coating operations such as plasma spray coating since considerable volume would be required and the standby workpieces would be subjected to contamination from the dust and side spray of the coating process.
Continuous conveyor systems are also utilized. These require a series of heavily pumped auxiliary chambers in tandem at each side, in and out. Danger of air contamination exists because the system is open to air through the auxiliary chambers.
Therefore, an object of the present invention is to provide a novel loading apparatus for a work chamber which allows continual processing of workpieces while attaining improved efficiencies in the loading and unloading of the workpieces.
A further object is to provide a loading apparatus for a work chamber operating with a controlled atmosphere, which allows loading and unloading of a workpiece while simultaneously processing another workpiece in the work chamber, with a minimal volume requirement for evacuating and/or replacing gas.
Another object is to provide a magazine type of loading apparatus suitable for a work chamber operating with a controlled atmosphere, which can be loaded and unloaded with a minimal volume requirement for evacuating and/or replacing gas.
Yet another object is to provide a loading apparatus for a work chamber in which workpieces are heated in a controlled atmosphere, which allows cooling time for a heated workpiece in the controlled atmosphere during subsequent operations in the work chamber and simultaneous reloading of other workpieces.